Panning And Scrolling; Initialization; Panning Right And Left; Scrolling Up And Down - Epson S1D13503 Series Technical Manual

EPSON

5.5 Panning and Scrolling

Panning and scrolling are typically used to show an image which is too large to be shown completely
on an LCD panel. Although the image is stored entirely in display memory, only a small portion is
actually visible on the LCD panel. This visible portion is called the viewport; the user moves this
viewport over different portions of the image by panning and scrolling. Panning moves the viewport
right or left. Scrolling moves the viewport up or down.

Initialization

To pan and scroll over a large image, the S1D13503 registers must first be initialized and the image
written to display memory. To do so, initialize the registers as described in Section 2, "Initializing
the S1D13503" on page 2, but with the following exception: the Address Pitch Adjustment Register
in the S1D13503 must be set to create a virtual display; see Section 5.1, "Virtual Displays" on page
27 for more information.

Panning Right and Left

To pan to the right, increase the value in the Screen 1 Display Start Address Register. To pan to the
left, decrease the value in the Screen 1 Display Start Address Register.
Note that the S1D13503 can pan right or left by either 1, 2, 4, 8, or 16 pixels. This is because the
Screen 1 Display Start Address Register refers to either bytes or words (see "S5U13503P00C Eval-
uation Board Display Memory" on page 24), and a byte can represent 1, 2, 4, or 8 pixels, and so a
word can represent 2, 4, 8, or 16 pixels; see Table 5-1 below:
Memory Interface
8 bits
16 bits

Scrolling Up and Down

To scroll up, increase the value in the Screen 1 Display Start Address Register by the number of
bytes in one virtual scan line. To scroll down, decrease the value in the Screen 1 Display Start
Address Register by the number of bytes in one virtual scan line.
A virtual scan line is in reference to a virtual display, in which an image larger than the physical size
of the LCD is stored. The number of bytes in a virtual scan line is the number of bytes required to
store one horizontal line of pixels in the virtual image.
Example 16
Scroll down one line for a 16 gray shade 640 x 200 virtual image using a 320 x 240
single panel LCD. The Memory Interface is set to 16 bits to support 128K of display
memory. Also describe how to scroll in a dual panel LCD.
1. Calculate the number of bytes in a virtual scan line.
Number of horizontal pixels in virtual image
------------------------------------------------------------------------------------------------------------------
Number of pixels per word
2-38
Table 5-1 Smallest Number of Pixels for Panning
Colors/
Pixels per Byte
Gray Levels
2
4
16
256
2
4
16
256
=
Smallest Number of Pixels for
8
4
2
1
8
4
2
1
640 pixels per scan line
------------------------------------------------------------- -
2 pixels per byte
Panning
8
4
2
1
16
8
4
2
= 320 bytes per scan line
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